In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on a pivotably-mounted actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.
Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of a magnetoresistive sensor stripe sandwiched between two magnetic shields that may be electrically connected together but are otherwise isolated. A current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.
The write element typically includes a coil of wire through which current is passed to create a magnetic field that can be directed toward an adjacent portion of the disk by a ferromagnetic member known as a write pole. While it is known that the write element can be arranged to either store data longitudinally or perpendicularly on the disk, most, if not all, commercial disk drives to date have utilized longitudinal recording arrangements. Although perpendicular recording techniques have the potential to allow for higher densities of recorded information, longitudinal recording is used in all current products for historical reasons. An early perpendicular recording technique is disclosed in U.S. Pat. No. RE33,949, the contents of which are incorporated herein by reference.
The '949 patent discloses a perpendicular or vertical write head with a write pole section, downstream shield section, and a pancake coil surrounding the write pole section to generate magnetic flux therein. The shield section is disclosed to have a surface facing toward the media that is many times larger than a similarly-oriented face of the write pole. The media is disclosed to include two layers, an upper layer closer to the head having perpendicular uniaxial. anisotropy and a lower layer having low magnetic reluctance (now known as the Soft Under Layer (SUL)). A high write field can then be produced between the write pole and the SUL to record information in the upper layer of the media. The write flux returns through the SUL to the downstream write shield.
Due to the pivotable mounting of the actuator arm, the angular alignment of the read/write head to a particular data track on the adjacent storage disk can vary based on the radial position of the data track on a disk. In other words, the angular alignment at a data track near the inner diameter of the media surface on the disk will be different than the angular alignment near the outer diameter of the media surface on the disk. This phenomenon is known as skew or the skew angle, and the profile of such skew angles across the different radial portions of the disk is known as the skew profile. As can be appreciated, depending on design criteria, it is possible for the disk drive system to be designed so that the relative angular alignment is optimal at the outer diameter and the greatest amount of skew angle is achieved at the inner diameter. Conversely, the design could optimize the skew angle at the inner diameter and have the least optimal skew angle at the outer diameter, or the optimal angular alignment could be achieved somewhere in between the inner or outer diameter. In modern disk drive systems, the worst-case skew angle may typically be in a range of 15 to 20 degrees (e.g., 17 degrees).
It should be understood that a primary difference between longitudinal recording and perpendicular recording is that with longitudinal recording the magnetic field is primarily generated in the write gap between the write pole tip and the return pole tip, while in perpendicular recording the magnetic field is primarily generated in the region between the write pole tip and the soft underlayer in the magnetic media. Thus, with perpendicular recording, the field will be generated in a cross-sectional area that corresponds to the footprint of the write pole tip appearing at the ABS. It can then be appreciated that it is desirable for the footprint of a write pole tip to be minimized. It can also be appreciated that significant skew angles produce a footprint that is skewed relative to the data recording track and creates a portion in the track where some of the data recorded is via side writing from a side edge of the footprint, which is undesirable. In order to reduce this effect, write pole tips for perpendicular recording may typically be trapezoidal in shape rather than rectangular. The side bevel angle on the write pole tip (the extent to which the lateral side of the write pole tip deviates from a 90 degree angle with the leading or trailing edge) determines the amount of bevel of the trapezoidal head. Unfortunately, there are limits to the amount of side bevel in a trapezoidal head that is desirable. Typically, it is not desirable to have a bevel greater than 10 degrees because of the lost cross-sectional area that a bevel creates, which reduces write flux, write field, and eventually areal density.
It is desirable to design a write head which does not suffer from the above drawbacks. It is against this background and a desire to improve on the prior art that the present invention has been developed.